The fact that diesel is only available at Furnace Creek WITHIN the park is not the disadvantage that it might seem. There is diesel to the east at Beatty, NV., Pahrump, NV., and at Panamint Springs, just outside the west boundary of the park. You could come in from Las Vegas via the Jubilee Pass road and come "up the gut" towards Furnace Creek; hitting Badwater, Devil's Golf Course, Artist's Drive, all in a half day. Then, fuel up in Furnace Creek and, head north to Mesquite Campground which will be slightly cooler than the Furnace Creek area. From there you have early access to Ubehebe Crater and out to the The Racetrack (must see!!). You could then stay out there at Homestead Dry Camp or retrace your route and head to the Wildrose, Thorndike and Mahogany Flat areas for a night. You would then exit via 190 to US 395, and get diesel again at Panamint Springs.
Do keep in mind that the passes over the Sierra Nevadas (except I-80) sometimes do not open up till June or July so a trip earlier forces one to use I-80 or come around the south end of the Sierras.
Once you are at Las Vegas, you can get pretty accurate weather reports for the days you might spend in DV. If it looks like it is going to be above 105, then skip it and continue south on I-15 and take CA-58 over to the west side of the Sierras, so you can access Sequoia and Kings Canyon on your way UP to Yosemite, and then to the Bay Area. Don't be scared off by the 134 statement; that was the RECORD high, recorded over a hundred years ago.
I have to say that the Grand Canyon, from either rim, is a disappointment after you have been to the viewpoints in Canyonlands National Park, especially The Needles Overlook. While the pines are scrubbier than on the GC rim, there are better pine areas than the GC really close to the Canyonlands overlooks.
But maybe you have been to Canyonlands already...............
